Thick composite magnetoelectric films by electrophoretic deposition

Electrophoretic deposition (EPD) from colloidal suspensions was utilized for the preparation of composite magneto-dielectric films on a conductive substrate. The present process is developed as a convenient forming process for the development of devices based on thick magneto-dielectric films [1]. The deposition parameters - using EPD - such as colloidal parameters, deposition voltage and deposition time and the post process parameters, such as drying velocity and sintering will be controlled. This work aims to control the fillers/matrix ratio during the deposition and obtain a good adhesion, compaction and functionality of the composite film after the heat treatment. Measurements results for the current transients during constant-voltage deposition and the correlated deposited mass are presented [2, 3].1] A.O. Karilainen, P.M.T. Ikonen, C.R. Simovski, S.A. Tretyakov, A.N. Lagarkov, S.A. Maklakov, K.N. Rozanov, and S.N. Starostenko, Experimental studies on antenna miniaturisation using magneto-dielectric and dielectric materials, IET Microw. Antennas Propag., vol. 5, no. 4, pp. 495–502, 2011. 2] C. Baldisserri, D. Gardini and C. Galassi, An analysis of current transients during electrophoretic deposition (EPD) from colloidal TiO2 suspensions, Journal of Colloid and Interface Science 347 (2010) 102–111 3] H. Farnoush, J.A. Mohandesi, D. H. Fatmehsari and F. Moztarzadeh, A kinetic study on the electrophoretic deposition of hydroxyapatite–titania nanocomposite based on a statistical approach, Ceramics International 38 (2012), 6753-676

Magnetoelectric composite bilayer film by electrophoretic deposition

In the recent years the interest of the research community towards multiferroic composite materials was growing fast [1,2]. A number of papers relates to bulk materials while less attention is focused on films. Electrophoretic deposition (EPD) was applied to prepare magnetoelectric (ME) composite bilayer thick films based on perovskite phase and spinel cobalt ferrite as some of the best piezoelectric and magnetostrictive oxides belong these crystal groups. The co-deposition of titanium oxide (TO) and cobalt ferrite (CFO) nanoparticles and the deposition of niobium-doped lead titanate zirconate (PZTN) were made from colloidal suspensions in ethanol keeping constant voltage and recording the current. Good adhesion and compaction of the green film were achieved by optimization of deposition voltage and time while high density of the film and minimized interphase reactions occurred after sintering. The deposited volume, the mixing of dielectric and magnetic phases and the density and ordering of the films have been verified by electron scanning microscopy after heat treatment. No reactions between the different phases was found. The piezoelectric properties were measured on the sintered films. [1] N.A. Spaldin, M. Fiebig, Science 309 (2005) 391. [2] R. Ramesh, N.A. Spaldin, Nat. Mater. 6 (2007) 21

Screen-printed piezoceramic thick films

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Tape cast PZT material with porosity gradient

Functionally graded porous Nb-doped PZT material (PZTN) was produced by addition of pore forming agents and tape casting. Stacked layers with different content of carbon black (CB) were co-fired and a porosity gradient was obtained. Tailoring the binder to plasticizer volume ratio of each single green layer, gradually increasing CB content and adjusting the binder burnout procedure are the critical issues to eliminate cracks and delaminations and develop crack-free porosity-graded multilayer with porosity ranging from 10 to 30 vol%. A load applied during the heating treatments was required to obtain a warpage-free, 400 ?m thick, planar multilayer specimen. Layers with different pore former content show different shrinkage values that can cause delamination or warpage during sintering. These differences are reflected in strain rate mismatch and can be influenced by the layer thickness and viscosity ratio. The piezoelectric properties of these materials are suitable for ultrasonic application

Heterostructured ceramic materials based on PZTN-CFO compounds

Multiferroic composites are currently one of the hot research topics [1]. Particulate ceramic composites have the advantages of low cost, simple production technology, good magnetoelectric effect and easy control of electrical and magnetic properties if the ferroelectric phase (generally a perovskite) and the ferromagnetic one (a ferrite with spinel structure) are mixed in a favourable proportion under the percolation threshold of the ferromagnetic phase. A great research effort is in progress to improve the fabrication of PZT–CoFe2O4 (PZT–CF) composites due to the excellent piezoelectric properties showed by the PZT material class and the large magnetostrictive coefficient of the CF. Unfortunately unwanted reactions occur during densification of PZT–CF materials at 1100-1200 °C. They are promoted by initial PbO loss that is calculated through XRD analysis, considering the amount of ZrO2 and variation of perovskite's tetragonality. The resulting titania reacts with CF to form cobalt titanate [2]. The microstructure of the composites at 26-81 mol % CF content was thoroughly investigated; the CF grain size distribution can be mono- or bi-modal and overgrowth [3] occurs. By setting a quite-fast sintering full densification and prevention of unwanted reactions was achieved for the PZT:CF 74:26 composites. The high coercivity (789 Oe) shown by these composites is correlated to the good dispersion of euhedral CF grains (250 nm) in the PZT matrix that is affected as well by limited grain growth (240 nm). [1] G. Schileo, Recent developments in ceramic multiferroic composites based on core/shell and other heterostructures obtained by sol-gel routes. Prog. Solid State Ch. 41 (2013) 87–98. [2] P. Galizia, et al., PZT-cobalt ferrite particulate composites: Densification and lead loss controlled by quite-fast sintering. J. Eur. Ceram. Soc. (2016). doi:10.1016/j.jeurceramsoc.2016.08.025 [3] P. Galizia, C. Baldisserri, C. Capiani, C. Galassi Multiple parallel twinning overgrowth in nanostructured dense cobalt ferrite. Mater. Design 109 (2016) 19–26. doi:10.1016/j.matdes.2016.07.05

Structure analysis of cobalt ferrite/titania composite

Magnetodielectric bulk composite of a magnetic phase and a dielectric one were tailored to tune the macroscopic properties of permittivity and permeability. The designing of heterostructure formed by magnetic and dielectric counterparts offers a versatile route for the production of isotropic composite material with unusual electromagnetic properties. This study investigates the microstructure of sintered titania (TO)/cobalt ferrite (CFO) composites related to compositional modifications. The crystalline structure was studied through the comparison of theXRD patterns withthe EDS analysis and the results of the image analysis done on the electron micrographs. The image analysis wasfundamental to verifythe XRD and EDS interpretations, and to measure the effective volume contentof the phasesafter heat treatment.Several TO/CFO ratios from 0.7 to 11.8were analyzed. The formation oftheternary compound (FCTO) was foundonly in the composite with the TO/CFO ratio equal or bigger than 3

Structure analysis of cobalt ferrite/titania-silica composite

Magnetodielectric bulk composite of a magnetic phase in dielectric matrix have been studied. Silica coated titania powder was produced by elctrocoagulation and used as dielectric matrix; while the cobalt ferrite powder was selected as magnetic filler. This study aims at tailoring the magnetic and dielectric phases and their interfaces in order to obtain new electromagnetic properties. The microstructure of sintered titaniasilica/cobalt ferrite composites has been related to compositional modifications in terms of silica/titania weight ratio and titania-silica/cobalt ferrite volume ratio. The crystalline structure was studied by XRD analysis supported also by EDS investigationand image analysis performed on the electron micrographs. The image analysis supported the XRD and EDS interpretations, and contributed to evaluate the effective volume contentof the phases after heat treatment

Magnetoelectric composite bilayer films by electrophoretic deposition

In the recent years the interest of the research community towards multiferroic composite materials was growing fast [1,2]. A number of papers relates to bulk materials while less attention is focused on films. Electrophoretic deposition (EPD) was applied to prepare magnetoelectric (ME) composite bilayer thick films based on piezoelectric phases and cobalt ferrite. The deposition/co-depositionwere made from colloidal suspensions in ethanolkeeping constant voltage and recording the current. Good adhesion and compaction of the green film were achieved by optimization of deposition voltage and time while high density of the film and minimized interphase reactions occurred after sintering. The chemical activity between the two layers was controlled through the batches composition and it could lead to the synthesis of complex engineered structures.The deposited volume, the mixing of dielectric and magnetic phases and the density and ordering of the films have been verified by electron scanning microscopy after heat treatment. The piezoelectric properties were measured on the sintered films. [1] N.A. Spaldin, M. Fiebig, Science 309 (2005) 391. [2] R. Ramesh, N.A. Spaldin, Nat. Mater. 6 (2007) 21

Elastic and dielectric measurements of the structural transformations in the ferroelectric perovskite (Na1/2Bi1/2)1-xBaxTiO3

NBT is a perovskite undergoing a series of structural and polar transitions starting from the high temperature paraelectric phase: tetragonal antiferroelectric, rhombohedral and finally ferroelectric. In solid solution with BaTiO3 the ferroelectric phase changes from rhombohedral to tetragonal, at the so-called morphotropic phase boundary, and the phases at higher temperature become ill-defined, also because of the large lattice disorder induced by the coexistence of differently charged cations in the same sublattice. Combined dielectric and anelastic spectroscopy measurements are presented, which clarify some issues related to the phase transitions in NBT-BT. The influence of Ba substitution on the tetragonal antiferroelectric phase is determined for the first time, and the possibility that a monoclinic phase, although with very short coherence length, exists near the morphotropic phase boundary is discussed in view of a large maximum of the elastic complianc